Semiconductor device

ABSTRACT

In a semiconductor device having a heat radiation plate, the tips of inner leads connected to a semiconductor chip have a lead width w and a lead thickness t, the width being less than the thickness. The inner leads are secured to the heat radiation plate. Fastening the inner leads to the heat radiation plate supports the latter and eliminates the need for suspending leads. A lead pitch p, the lead width w and lead thickness t of the inner lead tips connected to the semiconductor chip have the relations of w&lt;t and p≧1.2 t, with the inner leads secured to the heat radiation plate. The heat radiation plate has slits made therein to form radially shaped heat propagation paths between a semiconductor chip mounting area and the inner leads. In a molding member-sealed semiconductor device wherein the semiconductor chip is fixed to the heat radiation plate, the tip thickness t′ of the inner leads is made less than the thickness t of the other portions of the inner leads secured to the heat radiation plate.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a semiconductor deviceincorporating a lead frame. More particularly, the invention relates totechniques adapted advantageously to a semiconductor device with a leadframe comprising numerous leads as well as heat radiation plates.

[0002] LSIs and other semiconductor devices have known ever-higherlevels of circuit integration while incorporating higher functions andmore complicated circuits than ever before. The enhanced functionalityrequires furnishing each semiconductor device with a large number ofexternal terminals. This in turns involves increasing the number of padelectrodes provided on a semiconductor chip as well as the number ofleads, i.e., external terminals of the semiconductor device. A typicallogic semiconductor device may have hundreds of external terminals.Semiconductor devices of the so-called QFP (quad flat package) type,well known as a family of semiconductor devices each having numerousexternal terminals, are generally mounted on one side of a substrate andcalled surface-mounted semiconductor devices. The QFP type semiconductordevice is suitable for accommodating a large number of leads becauseeach of four sides of the package enclosing the semiconductor chip carrya plurality of leads. When mounted on a substrate, this type ofsemiconductor device permits an effective use of space around it.

[0003] A lead frame used in the assembling of such QFP typesemiconductors is discussed illustratively in “VLSI Packaging Techniques(Vol. 1)” published by Nikkei BP (in Japan) on May 31, 1993, pp.155-164. In particular, specific patterns of the frame are shown on pp.157 and 159.

[0004] Fine structures of the semiconductor chip comprise an increasingnumber of elements each operating at a higher speed than ever. Thiscauses an increase of heat generation from the semiconductor chip. Theproblem is avoided illustratively by a semiconductor device having aheat spreader, as described in the “VLSI Packaging Techniques” (Vol. 2),pp. 200-203. The semiconductor device has its semiconductor chipfurnished with a heat spreader arrangement to promote heat dissipationof the device.

SUMMARY OF THE INVENTION

[0005] In accommodating a large number of leads, the lead frame needs tohave its lead-to-lead spacing (i.e., lead pitch) narrowed and the widthof its leads lessened.

[0006] The semiconductor chip also comprises numerous pad electrodeswhose presence is necessitated by the enhanced functionality of thesemiconductor device. Meanwhile, the spacing between pad electrodes(i.e., pad pitch) has been reduced over the years. Whereas there aredifferent pad pitches for different semiconductor chips in general, theneed to obtain as many chips as possible per wafer involves establishingthe smallest possible chip size. The trend in turn requires having thesmallest possible pitch between pad electrodes.

[0007] Given such reduced pad pitches and under restrictions associatedtherewith, the process of bonding the many leads to the correspondingpad electrodes using wires made of gold or like material tends totrigger an increasing number of short-circuits between adjacent wires.

[0008] During resin molding after the wire bonding, a decline in themechanical strengths of leads or a narrowed wire spacing may let wiresbe deformed by molding resin fluidity. The deformation called wire flowcan result in short-circuited wires.

[0009] Furthermore, in a QFP, an area in which to lay out leads becomesnarrower the closer it gets to a centrally located semiconductor chip.The thickness and the pitch of the leads are subject to limitationsstemming from the limitation of the manufacture precision of the lead.More specifically, lead pitch cannot be made sufficiently fine comparedwith pad patch on the semiconductor chip. As the semiconductor chipshrinks in external dimensions, it becomes increasingly difficult tobring the tips of the leads close to the chip. When the lead tips to bebonded are distanced from the pad electrodes of the semiconductor chipunder such circumstances, wires for bonding the pads to the leads mustbe extended. Extended wires are likely to cause more short-circuits orresult in more wire flow than before.

[0010] While today's practical pad pitches are down to about 80 μm, therequired pitch is expected to reach 60 to 45 μm in the future. As chipsshrink further, bonding wires are extended correspondingly. At present,it is necessary to keep the wire length to a maximum of 5 or 6 mm inorder to ensure stable bonding. This requires further reducing the pitchof lead tips so as to avert wire extensions.

[0011]FIG. 1 shows results of simulations performed by the inventorsabout wire bonding. On 256-pin semiconductor chips with different padpitches, correlations were simulated between inner lead tip pitches onthe one hand and wire lengths for stable bonding on the other hand. Thesimulations revealed the need to restrict the lead tip pitch to amaximum of 180 μm with respect to the 60 μm pad pitch in order to ensurestable bonding.

[0012] Such micro-fabrication of the leads is bound to lower theirmechanical strength. Even an extremely limited amount of force can thusdeform the tenuous lead formation. The deformed leads triggershort-circuits.

[0013] A conventional solution to the above problem is the fastening ofinner leads using an insulating tape to prevent lead deformation. FIG. 2is a plan view of a conventionally structured tape fastened lead frame.FIG. 3 is a cross-sectional view of a resin-sealed semiconductor devicefabricated by use of the lead frame in FIG. 2.

[0014] The lead frame is illustratively made of a copper alloy. Asemiconductor chip 1 (indicated by broken lines) is fixed to a tab 2. Aplurality of leads 3 are located around the entire periphery of themounted semiconductor chip 1. The leads 3 come in two types: inner leads4 and outer leads 5. The tips of the inner leads 4 surround thesemiconductor chip 1.

[0015] The leads 3 are integrated with a dam bar 6 or with a tie bar 8constituting a framework of the lead frame. The inner and outer leads 4and 5 are formed inside and outside of the dam bar 6 respectively. Thetab 2 is supported by tab suspending leads 7 furnished across the innerleads 49. The inner leads 4 and the tab suspending leads 7 are fastenedto a rectangular insulating tape 9.

[0016] In the case of a semiconductor device using the above-describedlead frame, the semiconductor chip 1 is fixed to the tab 2 by resin orby silver paste while the inner leads 4 are connected to pad electrodes10 of the chip 1 by bonding wires 11. After bonding, the semiconductorchip 1, tab 3, inner leads 4 and bonding wires 11 are molded by amolding member 12 illustratively made of epoxy resin. The dam bar 6 andtie bar 8 are cut so that the leads 3 are electrically isolated from oneanother. Thereafter, the outer leads 5 extending from the molding member12 are illustratively formed in gull wing fashion as shown in FIG. 3.This completes fabrication of the semiconductor device.

[0017] With the tape-fastened lead frame, as shown in FIGS. 2 and 3, amiddle part of the inner leads 4 is secured by the tape 9 to allow forflexible uses of the frame. In other words, the tape 9 is positionedaway from the tips of the inner leads 4. This is an inefficient andunstable structure for fastening the inner lead tips to which wires areto be bonded.

[0018] Furthermore, some recently developed semiconductor devices havebeen subject to significant heat generation from semiconductor chipsbecause of their enhanced functionality and high performance. Thesedevices have their semiconductor chips equipped with a heat radiationplate such as a heat spreader to facilitate heat dissipation.

[0019]FIG. 4 is a plan view of a lead frame for use with a heatspreader-incorporating QFP (called HQFP hereunder), wherein a copperfoil devised by the inventors is attached by adhesive to a semiconductorchip as a heat radiation plate. This setup has not been disclosed untilnow. FIG. 5 is a cross-sectional view of a semiconductor devicefabricated by use of the lead frame in FIG. 4.

[0020] As opposed to the lead frame and semiconductor device discussedearlier, this semiconductor chip 1 (indicated by broken lines) isfastened to a heat radiation plate 13. The inner leads 4 are also fixedto the heat radiation plate 13.

[0021] Such HQFP type semiconductor devices comprise numerous contactsbetween the molding member 12 and the heat radiation plate 13. Becauseof a feeble adhesive strength between resin (i.e., molding member 12)and metal (heat radiation plate 13), moisture absorbed in the interfacebetween the molding member 12 and the heat radiation plate 13 canevaporate and expand during reflow heating, causing a crack in thepackage. The reflow heating occurs during the process of mounting asurface-mounted semiconductor device onto a substrate. The semiconductordevice of FIG. 4 addresses the reflow problem by having a round holeprovided in the middle of the heat radiation plate 13, the hole allowingthe molding member 12 to contact the semiconductor chip 1. However, thisstructure is still not sufficient to overcome the problem.

[0022] It is therefore an object of the present invention to providetechniques for stabilizing the bonding of a semiconductor device havingnumerous leads.

[0023] It is another object of the present invention to providetechniques for preventing a crack in the package of a semiconductordevice furnished with a heat radiation plate.

[0024] A summary of typical ones of the invention disclosed in thepresent application will be described in brief in the following manner.

[0025] In a semiconductor device having a semiconductor chip fixed to aradiation plate and sealed by a sealant, the semiconductor chip beingconnected to tips of inner leads having a lead width of w and a leadthickness of t, wherein the lead width w is less than the lead thicknesst (w<t), and wherein at least the tips of the inner leads are fastenedto the radiation plate.

[0026] In a semiconductor device having a semiconductor chip fixed to aradiation plate and sealed by a sealant, the semiconductor chip beingconnected to tips of inner leads having a lead width of w and a leadthickness of t, wherein the lead width w is less than the lead thicknesst and wherein at least the tips of the inner leads are fastened to theradiation plate so as to support the radiation plate. This structureeliminates the need for installing conventional suspending leadssupporting the radiation plate.

[0027] In a semiconductor device having a semiconductor chip fixed to aradiation plate and sealed by a sealant, the semiconductor chip beingconnected to tips of inner leads having a lead pitch of p, a lead widthof w and a lead thickness of t, wherein the lead width w is less thanthe lead thickness (w<t), wherein the lead pitch p is equal to or lessthan 1.2 times the lead thickness t (p≧1.2 t), and wherein at least thetips of the inner leads are fastened to the radiation plate.

[0028] In a semiconductor device having a semiconductor chip fixed to aradiation plate and sealed by a sealant, the radiation plate havingslits made therein in a radial fashion forming heat propagation pathsradiating from a semiconductor chip mounting area on the plate towardinner leads.

[0029] In a semiconductor device having a semiconductor chip fixed to aradiation plate and sealed by a sealant, wherein tips of inner leads(tip thickness t′) are made thinner than the other portions of the innerleads (lead thickness t), and wherein at least the tips of the innerleads are fastened to the radiation plate.

[0030] In a method for fabricating a semiconductor device having asemiconductor chip fixed to a radiation plate and sealed by a sealant,the method comprising the steps of: connecting the semiconductor chip totips of inner leads having a lead pitch of p, a lead width of w and alead thickness of t, wherein the lead width w is less than the leadthickness t (w<t) and wherein the lead pitch p is equal to or less than1.2 times the lead thickness t (p≧1.2 t); fastening at least the tips ofthe inner leads to the radiation plate; and connecting the inner leadsto pad electrodes of the semiconductor chip.

[0031] In a method for fabricating a semiconductor device having asemiconductor chip fixed to a radiation plate and sealed by a sealant,the method comprising the steps of: making slits in the radiation platein a radial fashion forming heat propagation paths radiating from asemiconductor chip mounting area on the plate toward inner leads; andforming the sealant by letting it penetrate through the slits in theradiation plate during resin sealing.

[0032] In a method for fabricating a semiconductor device having asemiconductor chip fixed to a radiation plate and sealed by a sealant,the method comprising the steps of: fastening the semiconductor chip tothe radiation plate on a lead frame wherein tips of inner leads (tipthickness t′) are made thinner than the other portions of the innerleads (lead thickness t); and connecting the inner leads to padelectrodes of the semiconductor chip wherein at least the tips of theinner leads are fastened to the radiation plate.

[0033] In a lead frame comprising a plurality of leads and a radiationplate having a semiconductor chip mounting area onto which to fix asemiconductor chip, the semiconductor chip being connected to tips ofinner leads among the leads, the inner lead tips having a lead pitch ofp, a lead width of w and a lead thickness of t, wherein the lead width wis less than the lead thickness t (w<t), wherein the lead pitch p isequal to or less than 1.2 times the lead thickness t (p≧1.2 t), andwherein at least the tips of the inner leads are fastened to theradiation plate.

[0034] In a lead frame comprising a plurality of leads and a radiationplate having a semiconductor chip mounting area onto which to fix asemiconductor chip, the radiation plate having slits made therein in aradial fashion forming heat propagation paths radiating from thesemiconductor chip mounting area on the plate toward inner leads.

[0035] In a lead frame comprising a plurality of leads and a radiationplate having a semiconductor chip mounting area onto which to fix asemiconductor chip, wherein tips of inner leads among the leads (tipthickness t′) are made thinner than the other portions of the innerleads (lead thickness t), and wherein at least the tips of the innerleads are fastened to the radiation plate.

[0036] According to the present invention, there is provided asemiconductor device comprising: a heat radiation plate including a mainsurface and a back surface opposite to the main surface, the heatradiation plate having through type slits penetrating from the mainsurface to the back surface; a semiconductor chip having a semiconductorelement and a plurality of electrodes furnished on a principal plane,the semiconductor chip being fastened to the main surface of the heatradiation plate; a plurality of leads made of an inner lead and an outerlead each, tips of the inner leads being fixed to the heat radiationplate, the inner leads being connected electrically to electrodes of thesemiconductor chip; and a molding member sealing the heat radiationplate, the semiconductor chip, and the inner leads; wherein the throughtype slits are laid out in a radial fashion radiating from outside asemiconductor chip mounting area of the heat radiation plate toward aregion surrounded by the tips of the inner leads.

[0037] In the above semiconductor device, the beat radiation plate maybe rectangular in shape and the through type slits may be fabricated toextend toward four corners of the heat radiation plate.

[0038] Further, according to the present invention, there is provided asemiconductor device comprising: a heat radiation plate including a mainsurface and a back surface opposite to the main surface, the heatradiation plate having through type slits penetrating from the mainsurface to the back surface; a semiconductor chip having a semiconductorelement and a plurality of electrodes furnished on a principal plane,the semiconductor chip being fastened to the main surface of the heatradiation plate; a plurality of leads made of an inner lead and an outerlead each, tips of the inner leads being fixed to the heat radiationplate, the inner leads being connected electrically to electrodes of thesemiconductor chip; and a molding member sealing the heat radiationplate, the semiconductor chip, and the inner leads; wherein the throughtype slits are laid out in a radial fashion radiating toward a regionsurrounded by the inner leads on the heat radiation plate.

[0039] In the above semiconductor device, the through type slits may befabricated so that the back surface of the semiconductor chip ispartially exposed.

[0040] In the above semiconductor device, the heat radiation plate maybe rectangular in shape and the through type slits may be fabricated toextend toward four corners of the heat radiation plate.

[0041] As outlined above and according to the invention, the tips of theinner leads are fastened to the heat radiation plate. The structureeliminates the need for installing tab suspending leads supporting tabsthat carry the semiconductor chip. The area that was conventionallyallocated to the tab suspending leads is utilized for accommodating theinner leads. Given the same lead pitch, the structure allows the innerlead tips to be located closer to the semiconductor chip than before.

[0042] The inventive structure in which the inner lead tips are fastenedto the heat radiation plate stabilizes bonding and prevents deformationof the inner leads.

[0043] According to the invention, the heat radiation plate has slitsmade therein in a radial direction forming heat propagation paths. Thestructure enhances protection against the reflow problem whileminimizing a decline in heat radiation characteristic.

[0044] Also according to the invention, the inner lead tips are madethinner than before so as to improve accuracy in fabricating the tips.Fixing the inner lead tips to the heat radiation plate reinforcesresistance to the deformation of the tips.

[0045] These and other objects, features and advantages of the inventionwill become more apparent upon a reading of the following descriptionand appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is a graphic representation showing results of simulationsabout wire bonding;

[0047]FIG. 2 is a plan view of a conventionally structured tape-fastenedlead frame;

[0048]FIG. 3 is a cross-sectional view of a resin-sealed semiconductordevice fabricated by use of the lead frame in FIG. 2;

[0049]FIG. 4 is a plan view of a lead frame for HQFP use devised by theinventors;

[0050]FIG. 5 is a cross-sectional view of a resin sealed semiconductordevice fabricated by use of the lead frame in FIG. 4;

[0051]FIG. 6 is a plan view of a lead frame practiced as an embodimentof the invention;

[0052]FIG. 7 is a cross-sectional view of a resin-sealed semiconductordevice fabricated by use of the lead frame in FIG. 6, the view beingtaken on line A-A′ in FIG. 6;

[0053]FIGS. 8A and 8B are cross-sectional views of tips of inner leadson the lead frame in FIG. 6;

[0054]FIGS. 9A and 9B are cross-sectional views of tips of inner leadson the lead frame in FIG. 2;

[0055]FIG. 10 is a graphic representation comparing different types ofslits in terms of thermal resistance;

[0056]FIG. 11 is a combination of a plan view and a cross-sectional viewshowing how inner lead tips or pad electrodes of a semiconductor chipare laid out;

[0057]FIG. 12 is another combination of a plan view and across-sectional view depicting how inner lead tips or pad electrodes ofa semiconductor chip are laid out;

[0058]FIG. 13 is another combination of a plan view and across-sectional view illustrating how inner lead tips or pad electrodesof a semiconductor chip are laid out;

[0059]FIG. 14 is another combination of a plan view and across-sectional view indicating how inner lead tips or pad electrodes ofa semiconductor chip are laid out;

[0060]FIG. 15A is a plan view of a lead frame with differently shapedslits in the heat radiation plate;

[0061]FIG. 15B is a cross-sectional view of a resin-sealed semiconductordevice fabricated by use of the lead frame in FIG. 15A, the view beingtaken on line B-B′ in FIG. 15A;

[0062]FIG. 16 is a plan view of another lead frame with differentlyshaped slits in the heat radiation plate;

[0063]FIG. 17 is a plan view of another lead frame with differentlyshaped slits in the heat radiation plate;

[0064]FIG. 18 is a plan view of another lead frame with differentlyshaped slits in the heat radiation plate;

[0065]FIG. 19 is a plan view of another lead frame with differentlyshaped slits in the heat radiation plate; and

[0066]FIG. 20 is a cross-sectional view of a variation of theembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] Preferred embodiments of this invention will now be describedwith reference to the accompanying drawings. Throughout the drawings,like reference characters designate like or corresponding parts, andtheir descriptions are omitted where they are repetitive.

[0068] (First Embodiment)

[0069]FIG. 6 is a plan view of a lead frame for an HQFP typesemiconductor device practiced as a first embodiment of the invention.FIG. 7 is a cross-sectional view of a semiconductor device fabricated byuse of the lead frame in FIG. 6, the view being taken on line A A′ inFIG. 6. FIGS. 8A and 8B are cross-sectional views of tips of inner leadson the lead frame in FIG. 6. FIG. 8A shows lead tips formed by etching,while FIG. 8B shows lead tips formed by press.

[0070] The lead frame is made illustratively of an Fe-Ni alloy or acopper alloy. The entire periphery of a semiconductor chip 1 (indicatedby broken lines) is surrounded by tips of inner leads 4 among aplurality of leads 3. The leads 3 are integrated with a dam bar 6 orwith a tie bar 8 constituting a framework of the lead frame. An insideand an outside portion of the dam bar 6 make up the inner leads 4 andouter leads 5 respectively. The semiconductor chip 1 is bonded fixedlyto a beat radiation plate 13 using polyimide type adhesive 14 and diebonding agent 17. The inner leads 4 are fastened to the heat radiationplate 13 by use of the adhesive 14.

[0071] In the case of a semiconductor device using the above-describedlead frame, the semiconductor chip 1 is fixed to the heat radiationplate 13 by resin or by silver paste 17 while the inner leads 4 areconnected to pad electrodes 10 of the chip 1 by bonding wires 11. Afterthe bonding, the semiconductor chip 1, heat radiation plate 13, innerleads 4 and bonding wires 11 are sealed by a molding member 12illustratively made of epoxy resin. The dam bar 6 and tie bar 8 are cutso that the leads 3 are electrically isolated from one anotherThereafter, the outer leads 5 extending from the molding member 12 areillustratively formed in a gull wing shape or in other appropriatemanner. This completes fabrication of the semiconductor device 21.

[0072] On an etched lead frame, the lead top width is made greater thanthe lead bottom width so that the lead tops will be wide enough toaccommodate bonding while the lead width w is minimized. To produce sucha cross-sectional structure illustratively requires altering etchingconditions on the tops and bottoms of the leads.

[0073] At the lead tips where the lead pitch p is narrow, the leadthickness t is less than the lead width w. This lead structure tends tosuffer from poorly fastened wires at the time of bonding and isvulnerable to crosswise deformation It follows that on a lead framewhere the pitch of the inner lead tips is 180 μm, i.e., 1.2 times thelead thickness or less, the inner leads 4 are preferably fixed to theheat radiation plate 13.

[0074] With the inner leads 4 fixed to the heat radiation plate 13, thelead tips are kept anchored during wire bonding. This ensuresreliability of wire bonding. The benefit is corroborated by comparisonwith cross-sectional views of FIGS. 9A and 9B showing inner leads 4 ofthe lead frame in FIG. 2.

[0075] Today, lead frames are approximately 150 μm in thickness, aboutas thin as they can get in the face of possible deformation of the outerleads 5. The lead pitch is typically 185 μm, the lead width 100 μm, andlead spacing 85 μm. In the future, on lead frames with a narrow leadpitch, the lead pitch at the tips of the inner leads 4 will be 180 μm orless. Likewise the lead width w is expected to be less than the leadthickness (w<t) and the inner lead tip pitch p to be equal to or lessthan 1.2 times the lead thickness t (p≧1.2 t). In such cases, accordingto the invention, the inner leads 4 are to be fixed to the heatradiation plate 13 on the lead frame to keep the lead tips anchoredduring wire bonding. The structure should enhance the reliability ofwire bonding.

[0076] On the lead frame of the invention, the semiconductor chip 1 isfastened to a semiconductor chip mounting area on the heat radiationplate 13 fixed by the inner leads 4. In this setup, there are no tabsuspending leads furnished conventionally to support tabs on which tomount a semiconductor chip. Regions where the tab suspending leads usedto be provided are utilized for the layout of inner leads 4.

[0077] In the setup above, the corners where tab suspending leads wereconventionally furnished also accommodate inner leads 4. Given the samelead pitch, it is thus possible to locate the tips of the inner leads 4closer to the semiconductor chip 1 than before. This in turn shortensthe lengths of wires to be bonded after the semiconductor chip 1 ismounted. As a result, wire deformation is minimized and short-circuitsbetween wires are reduced during sealing by use of resin.

[0078] It is also possible to widen the lead pitch or increase thenumber of leads without getting the tips of inner leads 4 coming closerto one another.

[0079] Slits 15 are made in the heat radiation plate 13 between the areaon which to mount the semiconductor chip 1 on the one hand and the innerleads 4 on the other hand. The slits 15 allow the molding member 12 topenetrate through the heat radiation plate 13 and make it difficult forthe plate 13 and the molding member 12 to separate. With the moldingmember 12 penetrating the heat radiation plate 13, an enhanced level ofresistance to the reflow problem is attributable to two reasons: anincreased force of the molding member holding down the semiconductorchip 1, and a separated interface between the heat radiation plate 13and the molding member 12 also disconnecting forces caused byevaporation and expansion of the moisture content. The semiconductorchip 1 to be mounted varies in size depending on what is specificallyrequired of it in function. In this embodiment, the semiconductor chips1 and the slits 15 are unchanged in their sizes. When a largersemiconductor chip is to be mounted, edges of the chip are partiallyoverlaid with the slits 15, and the chip is secured by the resin 12.

[0080] The slits 15 are shaped so that heat propagation paths X of theheat radiation plates 13 are formed in radial direction, as indicated byarrows X. Illustratively, putative conventional slits 16 indicated bybroken lines as perpendicular to the heat propagation paths X, shownhere for reference, will interrupt propagation of heat along the pathsX. FIG. 10 is a graphic representation comparing different types ofslits in terms of thermal resistance. In FIG. 10, the inventive slitsetup represented by slit 15 and the conventional slit setup denoted byslit 16 are compared with a setup of no slit. It can be seen that theinventive slit setup 15 keeps a rise in thermal resistance smaller thanthe other setups and minimizes the possibility of deterioration causedby heat dissipation.

[0081] With the HQFP type semiconductor device described above, the tipsof the inner leads 4 or the pad electrodes 10 of the semiconductor chip1 may be laid out in an alternately arrangement (staggered fashion). Thestaggered layout provides further reliability in bonding wires.

[0082] Conventionally, as shown in FIG. 11 (a plan view on the right anda cross-sectional view on the left), the tips of the inner leads 4 orthe pad electrodes 10 of the semiconductor chip 1 are arranged in asingle row along each side of the chip 1. According to the invention, asshown in FIG. 12 (a plan view on the right and a cross-sectional view onthe left), the adjacent pad electrodes 10 of the semiconductor chip 1may be laid out alternately arranged (staggered) along each side of thesemiconductor chip 1, with wires bonded at different elevations to theelectrodes. The layout makes the bonding of wires to the pad electrodes10 easier than before.

[0083] Likewise, as illustrated in FIG. 13 (a plan view on the right anda cross-sectional view on the left), the tips of the adjacent innerleads 4 may be laid out staggered, with wires bonded at differentelevations to the lead tips. Furthermore, as depicted in FIG. 14 (a planview on the right and a cross-sectional view on the left), the tips ofthe adjacent inner leads 4 as well as the adjacent pad electrodes 10 ofthe semiconductor chip 1 may be laid out staggered, with wires bonded atdifferent elevations to the lead tips and the electrodes. The layoutmakes it easier than before to bond wires to the inner leads 4 and padelectrodes 10.

[0084] The slits 15 to be furnished in the heat radiation plate 13 maytake diverse patterns as shown in FIGS. 15A through 19.

[0085] Pattern examples shown in FIGS. 15A and 17 give priority to theresistance to the reflow problem by enlarging the area for the slits 15,while an example in FIG. 16 favors an enhanced capability of heatdissipation because the slits 15 are made narrower than those in FIG.15A and FIG. 17 so as to enlarge the paths for heat dissipationcorrespondingly. A pattern example in FIG. 18 seeks a trade-off betweenresistance to the reflow problem and better heat dissipation. The slits15 in FIG. 16 are shaped in such a manner that sufficient heatdissipation is guaranteed while the resistance to the reflow problem isimproved. The slit pattern in FIG. 15A and that in FIG. 17 are similarin shape and different in orientation. In the pattern of FIG. 15A, themolding member 12 provides higher resistance to the reflow problem bysecuring the corners of the semiconductor chip 1, i.e., by anchoring thechip corners with resin. In the pattern of FIG. 17, a widened area ofcontact between the semiconductor chip 1 and the heat radiation plate 13ensures a better heat dissipation characteristic. A suitable slitpattern may thus be selected depending on what is particularly requiredof the semiconductor device. FIG. 15B is a cross-sectional view of asemiconductor device fabricated by use of the lead frame in FIG. 15A,the view being taken on line B-B′ in FIG. 15A. In FIG. 15B, the partsalready shown in FIG. 7 are given the same reference numerals, and theirdetails are omitted. Some portions of the back of the semiconductor chip1 are not overlaid with the heat radiation plate 13; these portions aresealed directly by the sealing resin 12.

[0086] The slits 15 in the pattern example of FIG. 19 are identical inshape to those in FIG. 15A. The difference is that the tips of the innerleads 4 in FIG. 19 are laid out in an alternately arrangement to makethe bonding of wires easier. That layout of the inner leads 4 may alsoapply to the other examples having the different slit shapes in FIGS. 16through 18. The same also applies to the pad electrodes 10 of thesemiconductor chip 1. Illustratively, a semiconductor chip 1 with itspad electrodes 10 laid out staggered as shown in FIG. 12 may be appliedto the lead frames in FIGS. 15A through FIG. 19.

[0087]FIG. 20 shows a variation of this embodiment wherein the tipthickness t′ of the inner leads is made greater than the thickness t ofthe other portions of the leads 3. Such partially different leadthicknesses may be acquired illustratively by localized etching. Whenthe leads are to be fabricated, their thickness constitutes an importantfactor in precision. That is, the accuracy of lead fabrication isensured by making the tips of the inner leads 4 thinner than before(i.e., where precision counts); the remaining lead portions are madesufficiently thick to guarantee sturdiness. When the tips of the innerleads 4 are thinned for accuracy, it is important to fasten the leads tothe heat radiation plate 13 to prevent their deformation.

[0088] Although the description above contains many specificities, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of the presently preferred embodiment ofthis invention. It is to be understood that changes and variations maybe made without departing from the spirit or scope of the claims thatfollow.

[0089] For example, although the embodiment above was shown havingrectangular heat radiation plates on which to secure the leads, this isnot limitative of the invention. Alternatively, the heat radiationplates may be circular. Such round heat radiation plates have theadvantage of smoother resin flow during resin molding, which reduces theincidence of voids inside.

[0090] The heat radiation plate of the embodiment above may be equippedwith a bonding area for bonding to ground. This arrangement makes up alead frame ready for bonding to ground, which further enlarges the scopeof applications for the inventive semiconductor device.

[0091] There need not be a single semiconductor chip to be mounted onthe heat radiation plate. Alternatively, a plurality of semiconductorchips may be mounted on the heat radiation plate. That is, the inventionalso applies advantageously to multi-chip semiconductor devices.

[0092] Although the description above has dealt primarily with the fieldof semiconductor devices constituting the technical background of thisinvention, that field is not limitative of the invention. The presentinvention also applies extensively to devices wherein electroniccomponents are installed using lead frames.

[0093] The major effects of this invention as disclosed herein aresummarized below.

[0094] (1) According to the invention, the tips of the inner leads aresecured to the heat radiation plates.

[0095] (2) The feature (1) above offers the benefit of stabilizing thebonded wires.

[0096] (3) The feature (1) above also prevents deformation of the innerleads.

[0097] (4) According to the invention, the tips of the inner leads arelaid out at equal intervals on all sides of the semiconductor chipmounting area. The layout offers the benefit of locating the inner leadtips closer to the semiconductor chip mounting area than before.

[0098] (5) The feature (4) above shortens the wires to be bonded.

[0099] (6) According to the invention, the heat radiation plate hasslits made therein in a radial fashion forming heat propagation paths.The structure enhances protection against the reflow problem.

[0100] (7) According to the invention, the slits made in the heatradiation plate in a radial fashion forming heat propagation pathsminimize a decline in heat radiation characteristic.

[0101] (8) Also according to the invention, the inner lead tips are madethinner than before so as to improve accuracy in fabricating the tips.

[0102] (9) Further according to the invention, the inner lead tips aremade thinner than before and secured to the heat radiation plate. Thisstructure prevents deformation of the inner lead tips.

What is claimed is:
 1. A semiconductor device comprising: a heatradiation plate including a main surface and a back surface opposite tosaid main surface, said heat radiation plate having slits penetratingfrom said main surface to said back surface; a semiconductor chip havinga semiconductor element and a plurality of electrodes furnished on aprincipal plane, said semiconductor chip being fastened to said mainsurface of said heat radiation plate; a plurality of leads each havingan inner lead and an outer lead, tips of the inner leads being fixed tosaid heat radiation plate, said inner leads being connected electricallyto electrodes of said semiconductor chip; and a molding member sealingsaid heat radiation plate, said semiconductor chip, and said innerleads; wherein said slits are laid out in a radial direction radiatingfrom outside a semiconductor chip mounting area of said heat radiationplate toward a region surrounded by said tips of said inner leads.
 2. Asemiconductor device according to claim 1, wherein a tip lead width w ofsaid inner leads is less than a lead thickness t of said inner leads. 3.A semiconductor device according to claim 2, wherein a tip lead pitch pof said inner leads is equal to or less than 1.2 times said leadthickness t of said inner leads.
 4. A semiconductor device according toclaim 2, wherein a tip lead thickness t′ of said inner leads fixed tosaid heat radiation plate is less than said lead thickness t of saidinner leads.
 5. A semiconductor device according to claim 1, whereinsaid slits are fabricated in such a manner that heat propagation pathsare formed radially in said heat radiation plate.
 6. A semiconductordevice according to claim 1, wherein pads of said electrodes are laidout in an alternately arrangement on said semiconductor chip.
 7. Asemiconductor device according to claim 1, wherein said tips of saidinner leads are laid out in an alternately arrangement.
 8. Asemiconductor device according to claim 1, wherein said heat radiationplate is rectangular in shape and said slits are fabricated to extendtoward four corners of said heat radiation plate.
 9. A semiconductordevice comprising: a heat radiation plate including a main surface and aback surface opposite to said main surface, said heat radiation platehaving slits penetrating from said main surface to said back surface; asemiconductor chip having a semiconductor element and a plurality ofelectrodes furnished on a principal plane, said semiconductor chip beingfastened to said main surface of said heat radiation plate; a pluralityof leads each having an inner lead and an outer lead, tips of the innerleads being fixed to said heat radiation plate, said inner leads beingconnected electrically to electrodes of said semiconductor chip; and amolding member sealing said heat radiation plate, said semiconductorchip, and said inner leads; wherein said slits are laid out in a radialdirection radiating toward a region surrounded by said inner leads onsaid heat radiation plate.
 10. A semiconductor device according to claim9, wherein said slits are fabricated so that said back of saidsemiconductor chip is partially exposed.
 11. A semiconductor deviceaccording to claim 9, wherein said slits are fabricated in such a mannerthat heat propagation paths are formed radially in said heat radiationplate.
 12. A semiconductor device according to claim 9, wherein saidheat radiation plate is rectangular in shape and said slits arefabricated to extend toward four corners of said heat radiation plate.13. A semiconductor device according to claim 9, wherein pads of saidelectrodes are laid out in an alternately arrangement on saidsemiconductor chip.
 14. A semiconductor device according to claim 9,wherein said tips of said inner leads are laid out in an alternatelyarrangement.